Patent searches are typically performed at the USPTO. These searches may be performed by using the paper “shoes” at the USPTO libraries, by using the USPTO computer systems or by a combination of both. The USPTO maintains several branch libraries throughout the U.S.
A patent searcher may also perform a search on the USPTO website (www.uspto.gov). The USPTO website includes images of all U.S. patents and published patent applications to date. This is less common, however, because most experienced searchers are still based in Washington, DC. Also, the USPTO library includes many foreign art references and other tools that are not available online.
Many other governments and multi-governmental organizations contain their own online databases that include foreign applications. Some of the more popular and useful websites are WIPO (www.wipo.org), Espacenet (www.espacenet.com) or the German Patent Office (www.dpma.de).
Google also maintains a free patent database.
There are also a few commercial databases, such as Lexis-Nexis or Delphion, that include patents and other similar information that may be of interest to a patent searcher.